You do get what you pay for. The cheap ones are generally much heavier, so harder to pedal and dont have great geo for kids so they don't fir them properly and they break so don't last as long. We got dd1 a ByK one which dd2 now has and it is almost as good as new. We will be able to sell it after dd2 as well as they hold value.
Trying to convince DH about this now - I had convinced myself on a ByK one for DD (who won't ride a balance bike as she thinks are for babies, but wants to ride a bike - so she is going to have to learn using stabilizers and DS can go balance bike route) - but I hadn't actually checked out the price. We never buy anything for the kids so I am ok with it as am working, and would rather spend more money on a bike she will ride than less on one that is too heavy - I don't think she has much leg strength and she is heavy enough herself so think is important the bike is light.

How do you work out the size - looking at the height suggestions on the ByK site seems DD would need the 350 rather than 250 as she is about 107cm - does that sound right - they look kind of big. I am not that worried about it lasting her forever as DS can have it later or can sell it but just keen to get her riding.